Alternating current electromagnet



June 6, 1950 P. SALA ALTERNATING CURRENT ELECTROMAGNET 2 SheetsSheet 2Filed May 11, 1949 f a W/ o i I ma l m Hfm u m a PV Patented June 6,1950 ALTERNATIN G CURRENT ELECTROMAGNET Paolo Sala, Milano, ItalyApplication May 11, 1949, Serial No. 92,593 In Italy May 20, 1948 1Claim.

This invention relates to improvements in alternating current electromagnets and more particularly to magnets of the solenoid or suckingtype. Electro-magnets constructed for remote operated switches, forrelays or for other purposes, generally are of two types: those with asingle magnetic circuit and those with double magnetic circuit. In theformer, the U-shaped fixed part, carrying the induction coil upon alimb, and the U-shaped armature, make contact on two pairs of surfaceswhich must touch perfectly. These electro-magnets work, generally, withthe armature movable on a hinged bearing to cause rotation of thecarrier shaft of the electrical contacts. They have the well knowndefect that, with the armature opened, the two air gaps are difierent.Moreover, the necessity for having the two above mentioned pairs ofsurfaces meeting with perfect contact, presents mechanical difficulties.Furthermore, the use of these electro-magnets for the actuation ofswitches, compels the use of simple break switches, whereas the moderntendency is to make double break switches, because these ensure quickerand more eificient arc interruption with remarkable mechanicalsimplification. In the construction of simultaneous double breakswitches, the tendency has been towards the construction of the "doublemagnetic circuit sucking electromagnet, with three limbs on both thefixed and the movable part, and with the coil disposed on'the centralone, the movablepart moving always parallel to itself, instead ofrotating around an axis. In this case the electro-magnets couldbe-ca2lled iron-clad, because, as on the transformers of similar name,the circuits of the electro-magnetic flux are two, combining in thecentral limb, and subdividing in the two laterallimbs. This constructionis made by having generally both the fixed and the movable part ofE-sha-pe; this shape can be modifiedso that in the fixed part thecentral limb can be lengthened or shortened, relatively to the lateralones, the movable part having a complemental variation, so thateventually, one of the parts, generally the fixed one, can be U-shaped,and the other one consequently of T shape. This type of construction,whatever may be its geometrical accomplishment, presents always three:pairs of surfaces, that, technically should meet .on the closingof thearmature. Accurately .close meeting contact is not practically feasible,because of'the serious mechanical .difficulties relating to the grindingof the flat .contact surfaces. In practice, this .difficultyis overcomeby limiting the equirem n t a close m etin contact between the two pairsof lateral surfaces, leaving on the o t a t ny air ap, on the central lib, when the armature is closed. In any case, this is a very delic e opeat n, a ve sl ht mper cti ns or very slight increases of thisindispensable air can c use n i e ble l er nees n th el ct oma n coil Weand, by nsequenc e heating of the coil itself, vibrations and annoying,or, for several uses, even intolerable burns, during the operation ofthe device. The third defect is that in cutting the electro-magneticiron sheets, and for whatever shape of the electromagnet, there resultsan appreciable waste of raw material which sometimes surpasses theweight of the useful material. 7

In the last described type of construction as well as in that with thehinged armature two air gaps are formed in both electro-magnetic fluxcircuits when the core is opened, with a total stroke double that usedfor the stroke of the movable armature or core; this fact necessitatesan increase in the ampere turns of the actuating coil in order to getthe movable armature or core started.

The present invention avoids the above mentioned disadvantages anddefects by providing the alternate current sucking electro-magnet withself-adjusting pole pieces.

The invention consists in that the width of the unavoidable but unusedair gaps of the electro magnet for remote operated switches isconsiderably reduced, in order to make the latter more ready, rapid andefficacious and to limit in the meantime the current consumption. Thisis real.- ized practically by dividing the arms of the in!- vertedT-shaped core and placing the same so that they have only the functionof conveying the magnetic flux, while the central part has to efiec-tonly the useful movement for remote operated controls. Said arms of theinverted T effect only a light horizontal displacement in order tofollow the wide movement or the central part. The air gap closing occursautomatically because of magnetic sucking which produces selfadjustingof the component parts. If the arms of the inverted T-shaped core werejoined with the U-shaped fixed part of the electro magnet so as to forma C-shaped piece, after closing of the central part there would remainan air gap in any case for permitting the movable core central part atleast some vertical displacement, resulting in a considerable currentconsumption and efficiency reduction. The opening, on the contraryoccurs because of the central part fall- 3 ing by gravity at the momentof current interruption and because of wedgelike guide armatures withwhich the central part is provided.

The invention is illustrated by means of examples in the accompanyingdrawing wherein:

Figure 1 is a plan view of an electro-magnet in accordance with thepresent improvements but with a front outside or end plate removed,

Figure 2 is a side view of Figure 1,

Figure 3 is an end view as seen from the top of Figure 1,

Figure 4 is a top view of one of the self-adjusting pole pieces of theelectro-magnet,

Figure 5 shows in detail one of the magnetic iron sheets forming thefixed core,

Figure 6 shows in detail one of the iron sheets forming the movablecore,

Figure '7 shows in detail one of the magnetic iron sheets of theself-adjusting pole pieces,

Figures 8 and 9 are respectively a front view and a side view of one ofthe end plates of the laminated pole pieces, and

Figure 10 is a diagram of the two magnetic circuits.

Figure 11 shows the electro magnet with the movable core in off positionand Figure 12 shows the same in closing position after the snap actionproduced by the current in the bobbin.

In the drawing, the electro-magnet of the present invention, comprises afixed core formed by two packages of L-shaped magnetic iron sheets i,enclosed between end plates 2. The two L shapes are put together so asto form an inverted U as seen in Figure 1. The magnet further comprisesa movable core 3 of parallelopiped form composed of rectangular ironsheets packed between two end or outside plates l. In its movements thecore is guided by two guides 5 (Figure 3), the guidance being providedbetween the fixed end plates 2 and the iron sheets i. The fixed core iscompleted by two self-adjustin pole pieces 6 formed by magnetic ironsheets enclosed between two end plates '1 (Figures 4, '7, 8, 9). Thepole pieces =5 are separate from the lateral arms of the fixed core I(see Figure 1), and rest on two supports (not shown in the drawing),which may be placed, for instance, on the lower corners of the bentextensions of the end plates 2, so that they are very near to the twolower extreme surfaces of the fixed core I. These pole pieces aresupported so that they have freedom to move slightly as hereinafterexplained. The magnet coil (not shown in the drawing) is mounted in thespace 8 so that the core can move in the rectangular hollow of the coilspool. The end or outside plates l of the self-adjusting pole pieces 6,protrude beyond the laminae to contact the edges of the end plates 3 ofthe movable core, when the latter is at rest in the open position seenin Figure 1. Thus the polar surfaces of the two pole pieces 6, areslightly separated from the lateral surfaces of the movable core 3 inthis position. The end plates l of the movable core 3, present, on thelower parts of both sides, an inwardly inclined edge 9. At the moment ofexcitation of the coil, the movable core is attracted upwards, until ittouches with its upper surface the internal middle flat surface of thefixed core i. In the meantime, and because of the magnetic effecttending to eliminate the air gaps, the two self- ;adjusting pole pieces6 are attracted inwards, so that at the end of the stroke of the core 3,the inclined edges 9 of the plates 4 come opposite the appropriatelyshaped ends of the end plates T, and the pole pieces 6, being then free,move laterally 4 until they adhere and press strongly against the sidesof the movable core 3, at the same time the pole pieces 6 are attractedupwardly so that their upper external fiat surfaces adhere to the lowersurfaces of the limbs of the fixed core i. In this manner both magneticcircuits are completed in parallel (see Fig. 10), so that, besides theusual three pairs of contact surfaces, two more are formed between themovable core and the selfadjusting pole pieces, and the contact betweenthe various parts is perfect and with no air gap, and therefore withoutbreak of continuity in the magnetic circuits. In front of every surfaceof magnetic contact, in the hollows I ll (Figures 6, 7) are placed theusual anti-vibration short-circuiting rings ll Figure 4 and i2 Figure 1.When the electro-magnetic coil is de-energized, the core 3 falls and theend plates 7 move the pole pieces 6 outwards owing to the camming actionof the inclined edges 9 against the shaped ends of the plates l. Also,the pole pieces 5 cease to adhere to the lower faces of the pole piecesI. A small stop screw l3 (Figures 8 and 9) on each end plate 1 serves tolimit the movement of the self-adjusting pole piece 6 outwards becauseit comes against a suitable stop provided in the inner side of the endplates 2. The inverted U-shape of the movable core, constructed byputting together two I L-shapes, instead of making it in a single piece,

does not prejudice the continuity of the two parallel magnetic circuits,the junction between the L-parts being parallel and not transversal" tothe fiux, and therefore being of no effect upon the magnetic reluctanceof the two circuits- (Figure 10) On Figure 11 are to be noted theprincipal air gap i l corresponding to the stroke width of the movablecore 3 and very much reduced air gaps l5 necessary to permit sliding ofthe movable noted the movable core 3 raised to touch at the.

centre and fixed core I avoiding theair gap I 4, and the pole pieces 6,which because of the magnetic fiux and taking off the obstacle opposedby the package 4, whose portions 9 have received the ends it, have beenselfadjusted eliminating the air gaps l5 and in the meantime the air.

gaps ll.

When the electric circuit is reopened, the movable core 3 falls bygravity and the package 4 by wedging itself between the guides l6produces The electro magnet enlarging of pole pieces E3. returns then tothe off position shown on Figure 11. The vertical arrow f indicates thedirection of movement of movable core 3, while the horizontal arrows f1,f2 indicate the direction of movement of self adjusting pole pieces 6.

Of course, however, it is possible to construct the above mentionedfixed core of a single package of U-shaped iron sheets. The describedelectro-magnet presupposes single phase alternate: current feeding, butit is evident that it is easy,.

owing to the type of construction, to use also three phase alternatecurrent feeding, having beside the coil placed in the central part ofthe core,

two more coils on the sides of the fixed core. I I

The electro-magnet hereinbefore described presents the followingadvantages:

(i) Owing to the mobility of the two self-adjusting pole pieces 6, thevarious surfaces of magnetic contact, between fixed, semi-fixed andmovable parts, can adjust themselves naturally, to the exclusion ofevery air gap when the core is closed; this is absolutely impossible inthe usual types of iron clad cores, where the various contact parts arerigidly united together. In the electro-magnet of the present invention,the rigid union of parts is eliminated and substituted by aself-adaptability of the parts. Moreover, its construction permits ofobtaining very noiseless working, requiring no grinding of contactsurfaces and no calibration; this electro-magnet is therefore moresimple and cheaper than electromagnets with a single-piece core.

(ii) At the moment of the interruption of the excitation current in thecoil, as both magnetic circuits have three breaking points, instead oftwo, the residual magnetism is greatly reduced, and the movable core canbe very easily opened.

(iii) Owing to the elimination of every air gap, the coil wear isreduced to the minimum for an identical work duration, and coils withconstant wear are obtained for all devices of the same type. i 4

(iv) When the core is in the fully opened as.

tion, there is only one air gap corresponding to the working stroke ofthe core, instead of two as in the usual types, because the air gaps,corresponding to the free position of the self-adjustin pole pieces, areminimum and reduced to the engineering tolerances of the working of theparts. This becomes a very remarkable advantage for greater speed andfor attraction power, for an equal coil wear.

(v) Owing to the geometrical shapes of all the parts forming theelectro-magnet, they can be out without wasting raw material.

I claim:

An alternating current electro-magnet of the sucking type comprising aninverted, U-shaped, vertically divided fixed core, and an inverted T-shaped movable core located within and opposed to said fixed core andincluding a central body part and two separate and independently movableside parts extending transversely on either side of the lower end ofsaid central part, said central part and side parts being upwardlymovable, under the influence of magnetic flux, axially of the centralpart and the side parts also transversely of the central part, thelateral surfaces or" the central part and adjacent end surfaces of theside parts having oppositely inclined wedge surfaces cooperating todisplace said side parts outwardly when said central part movesdownwardly under the influence of gravity, thereby to displace said endsof said side parts from the downward path of movement of said centralpart.

PAOLO SALA.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,022,707 Smith Apr. 9, 19121,028,385 Price June 4, 1912 2,134,951 Piesker Nov. 1, 1938 FOREIGNPATENTS Number Country Date 17,676 France Oct. 2'7, 1913 640,233 FranceJuly 9, 1928

